Calibration of rolling mill screwdown position regulator

ABSTRACT

The screwdown position regulator of a rolling mill stand is usually calibrated in relation to a measured loaded roll opening or product thickness. Certain rolling mill arrangements, such as a two-stand reversing plate mill, include a length gage rather than a thickness gage at the stand, so some other method of maintaining screwdown calibration is required. The length measurements along with screwdown position and roll force measurements from two selected passes can be used in a constant volume relationship to determine the calibration of the screwdown system.

United States Patent Smith, Jr. 1 Jan. 18, 1972 [5 1 CALIBRATION F ROLLING MILL 3,387,471 6/1968 Freedman .1219 SCREWDOWN POSITION REGULATOR 3,253,438 /1966 Stringer ..72/l 2 [72] Inventor: Andrew W. Smith, Jr., Pittsburgh, Pa. Primary Examiner Milmn S Mehr [73] Assignee: weltlnghouse Electric Corporation, Pitt- Attorney-F. H. Henson and R. G. Brodahl sburgh, Pa. 22 Filed: Sept. 18, 1969 [57] ABSTRACT The screwdown sition re ulator of a rollin mill stand is 21 A I,N.: s59 s4 8 8 l 1 PP to usually calibrated in relation to a measured loaded roll opening or product thickness. Certain rolling mill arrangements, U.S. .-..72/8 such as a lwcygmnd reversing plate includ a length gage [51] 37/00 rather than a thickness gage at the stand, so some other [58] Field 0' Search ..72/8-l0, l6, [9, method f maintaining screwdown calibration is required' The 72/20 length measurements along with screwdown position and roll 56] Ram Clad force measurements from two selected passes can be used in a as constant volume relationship to determine the calibration of UNITED STATES PATENTS rev/down system- 3,348,393 /1967 Shipp ..72/8 12 Claims, 3 Drawing figures SCREWDOWN POSITION REGULATOR 9 4o 34 I SCREW V S1 T E c'T $R E mgnifl ROUGLQER 36 DIMENSION F GAUGE LQ E ga??? l6 0 r I -7-l LOAD 32 24- MILL MOTOR SPEED 26 CONTROL 1 PROCESS CONTROL COMPUTER PROGRAMME!) MANUAL INSTRUCTIONS INPUT CALIBRATION OF ROLLING MILL SCREWDOWN POSITION REGULATOR BACKGROUND OF THE INVENTION The rolling of wide plate is frequently done on a single-stand reversing mill. The desired fnal plate is usually much wider than the incoming slab, and therefore the rolling operation should include some initial broadside rolling in the direction which will increase the incoming slab width as well as some lengthwise rolling to produce the desired plate thicknem. A typical rolling sequence would begin with two light passes to break scale, and the slab would then be turned for the broadside rolling so the incoming slab width would at this time become the length and the incoming slab length would become the width. The broadside rolling would then proceed until the length is approximately equal to the desired plate width. The piece would then be turned again and the lengthwise rolling would proceed until the final plate thickness is obtained.

To control such a rolling mill operation, the screwdown or other system which makes it posible to adjust the roll opening must be calibrated in a precise manner. As the rolling proceeds, this calibration must be maintained in spite of roll wear and changes in the temperature of mechanical parts.

For a single-stand reversing plate mill this can be achieved by sensing the actual thickness of the product toward the end of the final rolling and comparing the actual thickness with the thickness derived from measured screwdown position and measured roll force. This actual thickness measurement is usually obtained from an X-ray radiation gage.

Such a mill would also include a length gage. The length gage would be used to check the length of the product being rolled during the broadside passes to detect any difference between the desired length and the actual length that would be caused by errors in the incoming slab dimensions, particularly the slab width.

Another arrangement for such a mill is to have two reversing stands. This allows for much higher production since the scale breaking and broadsiding passes may be performed in the early stand and the rolling for thickness can be performed in the later stand.

The sensors for such a two-stand reversing plate mill would be located as shown in FIG. 1 where the length measuring device 42 is located at the rougher l and the thickness-measuring device 46 is located after the finisher 12. The length gage on the rougher is useful to check the length dimension during the early broadsiding passes so that corrections can be made for variations in incoming dimensions. Since there is no means for measuring the thickness of the product being rolled in the roughing mill, this mill arrangement makes it more difficult to maintain the screw calibration on the stand where there is no X-ray gage.

A suitable optically operable apparatus for measuring the length dimension of the workpiece relative to the rolling mill can be of the type disclosed in U.S. Pat. No. 3,327,l25 of L. W. l-lerchenroeder and assigned to the same assignee as is the present invention.

It has been known in the prior art to provide a general length measurement during broadsiding to check on the original slab dimensions, as disclosed in an article by D. R. Jones and A. W. Smith that was published in the 1965 Iron and Steel Engineer Year Book at pp. 468 to 475 and in an article by Alonzo F. Kenyon that was published in the Nov., 1965 Westinghouse Engineer at pp. 182 to 187. This function is further described in an article by M. D. McMahon and M. A. Davis that was published in the 1963 Iron and Steel Engineer Year Book at pp. 726 to 733.

The roll force equation and mill stand stretch relationship for determining the unloaded roll opening of a rolling mill stand has already been explained in several published articles, for example one such article by J. W. Wallace appeared in the Mar. 1964 Westinghouse Engineer at pp. 34 to 40.

The use of an online digital computer control system including a model equation relating to the control process and stored in the memory unit of the computer is known to enable predictive control of the process and then adaptive control of the process relative to updating information obtained from actual operation of the process, for example a rolling mill. This permits a prediction of an individual stand roll force and operation relative to a given workpiece having a known grade and desired delivery gage. A suitable model equation is used to predict the roll force for each stand operation, and in relation to the reduction to be made in each stand operation to determine the unloaded roll opening for that stand operation. This general information is already known by persons skilled in this art and covered by several publications made by the applicant; for example, in the Iron and Steel Engineer Year Book for 1962 at pp. 587 to 592 is an article by A. W. Smith and L. P. Gripp dealing with this subject matter, and another related ar ticle by R. G. Schultz and A. W. Smith can be found in the Iron and Steel Engineer Year Book for l965 at pp. 46l to 467.

SUMMARY OF THE PRESENT INVENTION By measurement on a selected first measurement pass FMP of the workpiece through the rolling mill stand and within the operating range of a provided workpiece length dimension measuring device, the resulting measured length LM(FMP) of the workpiece out of the stand is measured and related to the roll force measured thickness l-IM( FMP) and the known or measured width WM(FMP). On a subsequent second measurement pass SMP through the rolling mill stand, and within the operating range of the workpiece length dimension measurement device, the resulting length measurement LM(SMP) for the latter pass is made. By equating the respective constant volume relationships in terms of the product of the height or thickness HM(SMP) times the length LM(FMP) on a given first measurement pass FM? and dividing this product by the length LM(SMP) on the subsequent measurement pass SMP, this enables the height HM(SMP) on the subsequent pass to be determined assuming there is no substantial change in width of the product.

There is no problem relative to the width, since it can be either measured or estimated and then included within the equation in both the numerator and denominator as respectively the first pass width WM(FMP) and the second pass width WM(SMP). The second pass width WM(SMP) on the subsequent pass SMP could be predicted by relating it to the previous first pass width WM(FMP) plus predicted spread, or the respective second pass width WM(SMP) could be measured by suitable sensing devices such as the dimension mea suring optical gage previously mentioned. lf the assumption is made that the width of the workpiece does not substantially change relative to each of these passes, this quantity can be left out of the calculation.

In this way, the length measurements on two different selected passes, preferably while performing the broadside rolling on a given piece, can be used to maintain screwdown calibration. This is possible since the reduction in thickness throughout the rolling should be accompanied by a corresponding increase in length. Any lack of agreement between the respective roll force measured thicknesses, as determined from sensed screwdown and roll force values, and the measured lengths can be attributed to errors in screwdown calibration.

The basic equation already known to persons skilled in this art for determining height, H, in relation to the unloaded screwdown roll position, SD, the established mill stand modulus, M, and the sensed stand roll force, F is as follows:

This same equation can be used before the making of a given pass to determine the proper screwdown position SD for that pass to produce a given height, H, for a roll force FP which has been predicted through operation of a suitable model equation.

Sufficient data is available from two separate broadside passes taken on a given piece, so the correlation between length and height can be checked by equating the volumes that are being delivered from each of these passes. The width in this equation can either be a measured width or an expected width using well-known techniques for predicting spread during the rolling process. The following equation relationship, using an asterisk to indicate multiplication, can now be set forth:

LM(SMP)'HM(SMP)*WM(SMP) 2) The data respectively is obtained during each of the first measurement pass, FMP, and the second measurement pass, SMP. The values for the measured heights, HM, in this equation can be replaced by the well-known roll force gagemeter equation:

HM=S DM+S+F M/ M i 3 i In this equation HM is the delivery height determined from measured screwdown SDM, and measured force FM, and in cluding the established offset 08 for calibration of the stand screwdown position detector. Substituting this value for HM in the above equation, and assuming no meaningful change in width occurred between the two passes such that the first pass width substantially equals the second pass width, and solving for the screwdown calibration offset OS:

LM(FMP) LM(SMP) (4) This screwdown calibration offset 08 can then be established and used to determine the proper screwdown position to produce desired or target delivery heights during subsequent rolling. This is done by using the latest determined value of offset 08, in the roll force gage equation and solving for the stand unloaded screwdown position SD, in relation to the model equation predicted roll force F and the desired target delivery height H, as follows:

In accordance with the teachings of the present invention this offset correction is provided for the screw position regulator of a given rolling mill stand such that a more meaningful screwdown position reading and setting for that stand is obtained. A direct-measuring workpiece dimension gage, such as a length gage, optically scans and thereby measures the actual length of the workpiece leaving the rolling mill stand on each of succeeding selected measurement passes through the rolling mill. This enables at least two related length readings to be taken on the same workpiece, and from these two length readings along with screwdown position and roll force measurements, any error in the screwdown position can be determined (equation 4). Thus, a determination of the actual thickness of the workpiece on the succeeding measurement pass can be made by using the reading of the screw position detector and roll force measurements. This error is removed by the introduction of an offset correction, for the purpose of improving the rolling by that stand of succeeding passes of the same workpiece or the rolling of subsequent workpieces.

With the given stand properly calibrated, a workpiece broadside length control operation can then take place in relation to a comparison made between a measured length of the workpiece for a selected pass and the target or desired length of the workpiece for that same pass. This comparison between these respective workpiece lengths is utilized to obtain an actual workpiece length from a selected succeeding pass through the given stand in accordance with a target or desired length of the workpiece after the latter pass. This is accomplished by a corresponding adjustment of the target delivery height for the latter pass and a corrected setting of the given stand screwdown position to provide that delivery height.

To still further improve the present calibration operation through the measurement of the length of the workpiece leaving the rolling mill stand by a remotely positioned device, there is included in the teachings of the present invention the keeping of a weighted average of this oflset correction to enable a converging error correction updating of the offset correction for subsequent operation of the rolling mill stand.

It is an object of the present invention to provide an improved screwdown position control arrangement for a rolling mill stand in relation to a remotely measured dimension of the workpiece delivered from that stand for a first pass of the workpiece through the stand as compared to the remotely measured dimension and operation of the rolling mill stand for a subsequent pass of the same workpiece through the rolling mill stand. A predetermined equation relationship including these quantities is established, and since each quantity in this equation relationship other than the offset 08 is known, and the offset remains substantially the same for succeeding passes, the equation can be solved for the unknown quantity 08. This is then introduced as a correction to improve the operation of the screw position determining apparatus.

BRIEF DESCRlPTlON OF THE DRAWINGS In FIG. 1 there is shown a diagrammatic arrangement of the control apparatus and method of the present invention;

In FIG. 2 there is shown an instruction program flow chart illustrating the operation of one embodiment of the control apparatus and method of the present invention; and

In FIG. 3 there is shown a flow chart illustrating another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODlMENT In FIG. I there is shown a rougher rolling mill stand 10 and a finisher rolling mill stand 12 of a typical plate rolling mill, which reduces a slab to a desired plate dimension by a plurality of reversed passes through one or more rolling mill stands, with two such rolling mill stands being illustrated in FIG. 1. The rolling mill stand 10 includes work rolls l4 and 16 and backup rolls 18 and 20, with a mill drive motor 22 operative to drive the rolls as determined by a mill motor speed control 24 operative with a process control computer 26. The latter may be of the general purpose digital type operative with a storage memory including a software program of instructions as provided from a suitable source of program instructions 28 and operative with a manual input 30 as well known to persons skilled in this art.

The digital process control computer 26 can include a central integrated process control or setup processor operative with a software sequentially stepped instruction program which is entered into and stored within the storage memory unit of the computer, and including associated input and output equipment such as generally described in an article entitled Understanding Digital Computer Process Control" by B. H. Murphy, which appeared in Automation for Jan. 1965, pp. 71 to 76, and in an article titled Small Control Computers- A New Concept by F G. Willard which appeared in the Westinghouse Engineer for Novv I964 at pp. 174 to 179. Two other articles of interest here in regard to the programming of a process control computer should also be noted; one was published in the Jan. 1965 Westinghouse Engineer at pp. l3 to 19 by Paul E. Lego and the other was published in the I966 Iron and Steel Engineer Year Book at pp. 328 to 334 by .l. S. Deliyannides and A. H. Green. Each computer processor is as sociated with predetermined input systems not specifically shown, which typically include a conventional contact closure input system which scans contact or other signals representing the status of various process operating conditions, a conventional analog input system which scans and converts process analog signals and operator controlled and other input devices and systems which could include paper tape, teletypewriter and dial input apparatus. Various kinds of information are en tered into the computer control system through information input devices including for example desired strip delivery thickness, grade of steel being rolled, any selected workpiece platicity tables, hardware-oriented programs and control programs for the programming system and so forth. The contact closure input system interfaces the computer control system with the process through the medium of measured or detected variables. To effect desired control actions, control devices are operated directly by means of output system contact closures or by means of analog signals derived from output system contact closures through a digital to analog converter. One such control action outputs from the computer control system the stand screwdown positioning command signals which are applied to the respective screwdown positioning regulator for each of the stands to determine the operation of the screwdown motor for desired screw positional movement at each stand. The previously determined mill spring modulus for each stand is stored in memory along with the calculated values of delivery height, theoretical length, length correction, change in offset, the offset deviation and the various other determined values set forth in the ilow charts. The calculated offset signal is sent to the screwdown position regulator to correct for the positional error of the associated screw apparatus for each stand. A suitable output display can be provided for operation with the computer control system in order to keep the mill operator generally informed about the mill operation and in order to signal the operator regarding an event or condition relative to any particular stand which may require some action on his part.

A load cell 32 is operative with the rolling mill stand for providing a reading of the roll force of the stand. A screwdown motor 34 is operative with a wellknown screw apparatus 36 in accordance with the operation of a screwdown position regulator 38 for determining the roll opening or the spacing between the work rolls l4 and 16 as well known to persons skilled in this art. A screw position detector 40 is operative to provide a feedback indication of the position setting of the screw apparatus 36. A dimension measurement gage 42, which may be optical in nature or respond to infrared radiation from a workpiece 44 operative with the mill stand I0, is operative with the process control computer 26 for providing an indication of at least one selected dimension, such as the length and even the width if desired, of the workpiece 44,

In the operation of a reversing mill such as here contemplated, a plurality of broadsiding passes are initially taken by the stand 10 to determine the final workpiece width. The schedule calculation made up in advance determines how many broadsiding passes are to be taken.

in relation to the operational flow chart of FIG. 2, step 100 is the start of the instruction programmed operation. In program step I02 the number of each successive present broadside pass about to be made is checked to see if it is the first, second or third broadside pass. If the present broadside pass is the first, second, or third pass, the step 104 sets the first length measurements pass LMP equal to zero and the computer counter setting 1, the number of times TL is calculated, is set equal to zero, and the program progresses to the step I06 which causes another pass of the workpiece to be made through the roll mill stand 10. When the number of the present broadsiding pass is greater than the third, for example the fourth broadside pass, the step 108 checks to see if the number of the present pass is too large such that it is now too late in the pass schedule and too close to the first pass for height FPF H.

Only during the broadsiding passes are the length measurements here made, and if the present pass through the mill is beyond a predetermined number of broadsiding passes then it is not desired that a length measurement be made in which case the program proceeds to step IIO where the offset 08 for calibration of the screw position regulator 38 is determined as the previous determined offset OS plus an offset deviation DOS already in memory storage; thereafter, the offset deviation DOS in memory storage is reset to zero. The program then progresses to the step I06, where a subsequent pass of the workpiece through the rolling mill stand is made.

If the step 108 determines that a suitable pass within the scheduled broadsiding operation is still taking place, the pro gram advances to the step 112 where a determination is made to see if the workpiece is on the wrong side of the mill; for example, for the particular rolling mill stand [0 shown in FIG. 1 the workpiece should be on the left-hand side of the rolling mill, as the workpiece happens to be after the even passes, for

a measurement of the length to be made by the dimension gage 42.

In the typical operation of a reversing mill stand 10 such as shown in FIG. 1, the first two passes of the slab through the rolling mill stand may be for scale breaking and passes 3 through 8 may be broadsiding passes. It is desired that the screwdown position regulator calibration in accordance with the present invention occur during these broadsiding passes, At least six broadsiding passes through the rolling mill stand are required to obtain the desired two length measurements of the workpiece leaving the rolling mill stand, including the two initial scale-breaking passes. The first pass for height for a given workpiece in this example would be pass 9, and the step I08 is operative to determine if the present pass through the rolling mill stand is greater than this first pass for height minus 1 which in this case would be the eighth broadsiding pass since it is desired that the screw position regulator calibration occur during the broadsiding. If the present pass is greater than pass 8, it is now in the first pass for height or beyond portion of the stand operation in which case it is no longer desirable to calibrate the screwdown position regulator. The offset devia tion DOS is used for pass 9 for correcting the screw position regulator offset, and for subsequent passes beyond pass 9 after this correction calibration has been made the deviation offset is set to zero; for example, for pass 10 and beyond DOS is no longer needed and would be zero.

The step 112 detemiines if the present pass is pass 4, 6, or 8 where a length measurement can be made with the dimension gage 42 positioned as shown in FIG. 1. If the present pass is an odd pass, the program advances to step I06 where another pass through the mill in initiated. Thusly when the present pass is an even broadside pass such as pass 4, 6, or 8, the program shown in FIG. 2 advances to step "4. In step 114 the measured height HM for pass N is calculated from the well-known roll force relationship previously set forth above as equation (3). The roll force FM(N) is indicated by the load cell 32 and the stand spring constant or modulus M is already known by past determination from stand operational data and stored in the memory of the process control computer 26. The value of the offset OS is obtained from the memory storage of the computer. The present pass N is generally indicated here, and this could be any one of the selected measuring passes, in this case 4, 6, or 8. The theoretical length of the workpiece 44 for pass N is calculated by the known volume of the workpiece 44 which is supplied as input data to the process control com puter 26 through the manual input 30 or a tape reader or the like. The measured height HM( N) has been calculated and the width W(N) is known as input data or is measured by a suitable provided dimension gage, which could be included as a second operation of the dimension gage 42 or an additional generally similar dimension gage operative with the width of the workpiece instead of the length of the workpiece could be provided. The measured length LM(N) is measured by the dimension gage 42, and a desired length correction LC is determined by dividing the measured length LM(N) by the calculated theoretical length L( N The program then proceeds to step 116 where a limit check is made to see if the length correction LC detemiined in step 114 is within a value limitation of :5 percent; if there is more than a 5 percent error in the measured length LM(N) present pass N as compared to the theoretical length L(N) for this same pass, the program proceeds to step 106 where the length correction calculated in step 114 is ignored and a next pass of the workpiece through the mill stand is made. On the other hand, if the length correction calculated in step [14 indicates no more than a plus or minus 5 percent error in workpiece length, the program advances to step I18 and a check is made of the value for the length measurement pass LMP in the memory of the process control computer to see if the length measurement pass is there set at zero. For the first three broadside passes through the rolling mill stand, LMP was set at program step 104 to zero, and if the stored value of LMP is still zero, this indicates that no previous measurement of workpiece length has been made.

If LMP is stored in the computer memory as zero when the check at step Us is made, the program advances to step 120 where a check is made to see if the present pass N is greater than the first pass for height minus 2. For purpose of example, this could be pas 9 minus 2 or pass 7, if present pass N is greater than pass 7, it is too late in the operation of the rolling mill stand to change the heights for the remaining broadsiding passes since the broadsiding is complete. The program advances to the step 106 and another pass of the workpiece through the rolling mill stand is executed. However, if the step 120 indicates that there are remaining broadside passes, the program advances to step 122. The length measurement pass LMP is now set in the memory as equal to N, and if present pass N is 6 for example, die length measurement pass LMP would be stored as 6 and the counter setting I would be stored as N-H or 7. n the other hand, for the case where the present pass N is 4 and therefore LMP is set equal to 4, 1 would be set to 4+] or 5. The program then advances to program step 124 where the next pass target height H( l) is now modified relative to the next pass I by the length correction LC calculated in step 114 such that the height for pass 5 (where the present pm is 4) is the previously scheduled height times the length correction LC. This would indicate that present pas 4 had the wrong actual delivery length and therefore the subsequent pass heights are adjusted.

For a better understanding of the function taking place at step 124, assume that the initially established rolling schedule called for a workpiece thickness or height of 5 inches and a length of 100 inches after the completion of present pass 4, which for this example would be the first measurement pass. The length correction LC is a ratio of the actually measured length LM(4), which for example might be 103 inches, to the theoretical length L(4), which would be 100 inches. Therefore, the length correction LC would be l03/l00 or L03. if the scheduled length for the next pass is I inches, this means that a theoretical and scheduled height of 4. l 7 inches should be realized after pass 5, by a volumetric relationship similar to that set forth in above equation (2). However, the fourth pass measured length is l03 inches indicating a length error to be corrected. Step 124 adjusts the target delivery height for the fifih pass to be (4.l7)"( 1.03) or 4.29 to correct this length error.

The program then advances to step 126 where a check is made to see if pass I is now the first pass for height FPFH minus I (such as pass 9 minus I which is 8); ifit is not, the program advances to step I28 where pass I is increased by l and a loop around operation occurs until the rescheduled height for the eighth pass is reached. This operation, for example, makes a recalculation of the height H for each of the subsequent passes, such as 5,6, 7, and 8 where l is 5 after the length measurement pass 4 and so forth; when l reaches the scheduled first pass for height FPFH minus I, the program advances to the step 106 where a subsequent pass of the workpiece is made through the stand 10.

In reference to the program step 118 if some numbered value is present for the length-measuring pass, and for the example of the first length measurement pass being pass 4, on the next or second measurement pass 6 the check at step 118 indicates that LMP is no longer zero so the program advances to step 130 where a calculation of screwdown calibration offset change TL is made in relation to the second measurement pm length gage reading LM(N), where N is now the second measurement pass 6, times the measured height HM( N) from the roll force equation times the known width MN) and minus the length gage reading LM( LMP) for the previous length measuring pass LMP (which for this example is the first length measuring pass 4) times the calculated height HM(LMP) for the previous length-measuring pass times the known width W( LMP) for the previous length-measuring pass, all divided by the length gage reading LM(LMP) for the previous length-measuring pass times the known width W(LMP) 'for the previous length-measuring pass minus the length gage reading LM(N) for the present measurement pass N times the width W(N) for the pass N. If die workpiece width for the second measurement pass SMP (which is here pass N) is assumed to be the same as the width for the first measurement pass FMP (which is here pass LMP) then the equation (4) above set forth is for the same relationship as here described.

The program then advances in step 132 where a limit check is made to see if the change in offset TL is greater than 25 mils negative. if this step is satisfied, the program advances to step 134 where a check is made to see if the change in offset TL is less than 25 mils. If the check made at program step 132 is not satisfied, then program step 136 limits the quantity TL to minus 25 mils, and if the program step 134 is not satisfied the program step 138 limits the change in offset TL to plus 25 mils. The instruction program then advances to step 140 where a weighted average is made. In step 104 the computer counter reading J was initially set at zero. In step [04 the quantity one is added to the previous counter reading, and the offset deviation DOS is calculated as any previous offset deviation, stored in the computer memory for previous offset change determinations for this workpiece, times J minus I, (which for the example of the second measurement pass 6 would be 1 minus 1 or zero) plus the change in ofi'set TL divided by 1. For the sixth pass the change in offset TL is set equal to the offset deviation since J is at this time a one value 1 represents a counter operation which increases by l for each length measurement pass, made during a given workpiece schedule of passes but not including the first length measure ment pass, for weighting purposes. The program advances to step such that as long as the rolling mill stand is still working on length measurement passes, the program advances to the program step 122 previously described for updating the delivery heights for the remaining passes.

The offset deviation DOS as established by the program step gives an average value of this offset deviation DOS. The program then advances first to steps [20 through 128 where the broadside heights are modified and then to step 106 where the offset deviation is added to the previous oflset value for determining the screwdown setting for subsequent passes of the workpiece through the rougher. The screwdown setting is determined in relation to the desired workpiece height minus the mill stand stretch, which is the predicted roll force divided by the mill spring constant or modulus for the stand, and minus the now modified offset; see equation (5) above set forth, for this relationship.

As a modification of the present invention for the situation where only two broadsiding passes are scheduled to be taken, if the original width of the workpiece was assumed to be 45 inches for the purpose of establishing the broadside height reduction schedule and the dimension measuring gage indicated the actual width to be 47 inches, the length correction LC can be initially determined as a measured 47 inches di vided by an assumed 45 inches. Since the scale-breaking pass or passes are made before a turn the width does not change, and afier passes l and 2 which are scale-breaking passes, the dimension gage 42 can be operative to measure the length of the workpiece which would provide the quantity LM( N) before the first broadside pass when the width is still the original width. At this time, for an assumed width is 45 inches, with the width measured by the dimension gage after the second broadside pass is 47 inches, then such an initial length correction can be determined as the now measured length LM(N) divided by assumed L(N), which is 47 divided by 45, to give a target length correction after the scale-breaking passes and before the broadsiding passes.

For example, in a typical operation of the rolling mill stand 10 shown in FIG. 1, the first and second passes through the mill would be scale-breaking passes, with the second pass positioning the workpiece 44 under the dimension gage 42, such that a width measurement could at this time be made to establish a target length correction. The third through eighth passes would be broadsiding passes, with the even passes numbered 4, 6, and 8 positioning the workpiece 44 under the dimension gage 42; as long as the program step 108 is satisfied in relation to the scheduled first pass for height FPFH permitting the length correction and offset change calculations to be made, the control operation in accordance with the present invention could take place for determining the length correction with the pass 4 being a first measurement pass LMP relative to pass 6 being a second measurement pass N for a second screwdown calibration calculation, and this same pass 6 could be a first measurement pass LMP relative to pass 8 being a second measurement pass N for a second screwdown calibration calculation. For this example, the ninth through additional passes would be passes for height operations afler a desired target broadside length is obtained.

In FIG. 3 there is shown a computer program flow chart which describes a more simple embodiment of the present invention. This program is initiated relative to every workpiece during the rolling of each pass in the roughing mill stand 10. The first two passes in a given workpiece rolling schedule are detected at step 103 and for these passes the value of the first measurement pass FMP, is set within computer memory to be at step 105. On the later passes when pass N is greater than 2, die check at step 107 detects odd passes where length measurements are not made because of the selected location of the length measuring device or dimension gage 42 shown in FIG. 1. For each even pass after pass 2, step 109 calls for the making of measurements for each of workpiece length stand screwdown setting and stand roll separating force. After the first measurement pass through the stand which would be pass 4 for the location of dimension gage 42, the check at step 1]] determines if FMP is equal to 0, and if it is the program advances to step 113 where the first measurement pass is now set in computer memory as equal to the pass number N. After pass 5 is executed, the step 107 would prevent the making of the process operation measurements as done in step 109. After pass 6 another set of similar measurements could be made at step 109, and since F MP is not zero as checked at step 11 l, the step 115 would set the second measurement pass S MP equal to the pass number 6. The offset OS would then be determined at step 117 using the measurements on each of the first measurement pass 4 and the second measurement pass 6 in accordance with the relationship set forth in above equation (4). This instruction program is arranged so that additional measurements would be made on each of the subsequent even pases, as long as the broadsiding passes last and a new value of offset is calculated each time that two suitable even measurement passes are available for comparison. A counter operation. such as the counter of FIG. 2, can be provided to keep track of the number of times the offset is determined. The value of the offset can then be filtered by the use of weighting factors, such as illustrated in FIG. 2, in order that errors in any particular readings will not give large excursions in offset values, but still be able to take care of the desired calibration correction for slow changes in screwdown calibration.

In general the accurate control of the cross rolling or broadside passes as well as later passes where the finish gage is to be controlled requires an accurately calibrated screwdown system. Roll wear and changes in mechanical equipment and in apparatus temperatures will cause the screwdowns to get out of calibration. An automatic correction determining means is needed to keep the screws calibrated. This calibration can be done if the actual delivery thickness of the delivered product from a given pass can be established relative to the stand screwdown position and roll force. A direct actual thickness measurement using an X-ray gage or the like is not always obtainable, particularly on a two-stand plate mill, where the cross rolling is performed in the first stand and the final rolling to thickness is done in the second stand. The length measurement made at the first stand can be used as here disclosed to calibrate the first stand screwdown system; to do this a measurement of roll force, screwdown position and workpiece actual length can be made on two related passes, assuming no spreading during these passes. The length on the first measurement pass FMP times the thickness or height for the pass FMP can be set equal to the length for the second measurement pass SMP times the thickness or height for the pass SMP. lf it is assumed the screwdown measurements have an error on all passes which we will call offset OS, each of the heights in the above equation can be replaced by the roll force equation relationship, where the delivery height for a given pass equals the unloaded screwdown plus the roll force divided by the stand mill spring constant but including and solving for the offset.

It would be desirable for the measurements to be made on successive passes, but it would be more common to have only a length gage on one side of the rougher mill as shown in FIG. 1. With the screwdown system properly calibrated, then any sensed error in the desired length of the workpiece at this time can be corrected by a corrected schedule for each remaining delivery workpiece height during the remaining broadside passes.

It is generally known and understood by persons skilled in this particular art of applying a computer control system such as shown in FIG. I that a combined hardware and software process control system comprises a special purpose extended control computer machine, and is provided when a general purpose computer is operated under the control of a software instruction program such as illustrated by the functional program flow chart of FIG. 2 and FIG, 3. Such a process control system can be built if desired using hardware or wired-logic programming, in view of the recognized general equivalence of a software programming embodiment and a hardware programming embodiment of substantially the same control system. However, when an involved industrial application such as here described becomes somewhat complex, the economics tend to favor the software approach due to the greater expense and lack of flexibility when logic circuits, such as well known NOR logic circuits, are wired together to provide the desired hardware programming circuit arrangement built up of such logic circuits to perform the sequential program steps set forth in the illustrated flow charts.

Although the present invention has been shown in relation to a specific embodiment, it should be readily apparent to those persons skilled in this art that various changes in form and arrangement of the described apparatus and operations may be made to suit the specific application requirements without departing from the spirit and scope of the present invention.

1 claim as my invention: 1. ln apparatus for controlling at least one stand of a rolling mill having a screwdown position control apparatus and a pair of rolls operative with a workpiece, the combination of;

means for establishing the delivery length of the workpiece after a first passage through at least said one stand of the rolling mill,

means for establishing the roll separating force and screwdown position of at least said one stand during said first passage, means for establishing the delivery length of said workpiece after a second passage through at least said one stand of the rolling mill,

means for establishing the roll separating force and screwdown position of at least said one stand during said second passage,

and means for determining the calibration of said screwdown position control apparatus using a predetermined workpiece volume relationship relative to said first and second passage through the rolling mill.

2. The apparatus of claim I, including said means for determining the calibration of said screwdown position control apparatus being operative with the assumption that the workpiece width remains substantially the same during said first and second passage.

3. The apparatus of claim 1, including said means for determining the calibration of the screwdown position control apparatus using nominal width and a prediction of the increase in width during rolling.

4. ln apparatus for controlling a rolling mill having a pair of rolls operative with a workpiece, the combination of:

means for establishing the delivery length and width of said workpiece afier a first passage through said rolling mill,

means for establishing the roll separating force and screwdown position, of said rolling mill during said first passage, means for establishing the delivery length and width of said workpiece after a second e through said rolling mill,

means for establishing the roll separating force and screwdown position of said rolling mill during said second passage,

means for determining the calibration of the rolling mill screwdown position using a predetermined workpiece relationship between the first and second passage through the rolling mill. 5. ln apparatus for controlling at least one stand of a rolling mill having a pair of rolls operative with a workpiece, the combination of:

means for establishing the value of a selected dimension of said workpiece after a first reduction of said workpiece by passing said workpiece between the rolls of said rolling mill,

means for establishing the value of said selected dimension of said workpiece after a second reduction of said workpiece by passing said workpiece between the rolls of said rolling mill,

means for establishing an operational error condition of at least said one stand in relation to said selected dimension established after said first reduction and said selected dimension established after said second reduction,

means for predicting a desired value of said selected dimension after a predetermined pass of said workpiece between said rolls,

and means for establishing the roll opening position of at least said one stand during said predetermined pass in accordance with said operation error and in accordance with said desired value of said selected dimension.

6. The apparatus of claim 5, with said selected dimension being the length dimension of said workpiece,

and with said predetermined pass being a subsequent pass of said workpiece between said rolls.

7. ln apparatus for controlling the roll opening position of a rolling mill stand operative with a workpiece, the combination of:

means for meauring a first dimension of said workpiece after each of a first passage through said stand and a second passage through said stand,

means for establishing a second dimension of said workpiece after each of said first passage and said second passage in relation to the stand roll forces during the respective first passage and second passage through said stand,

means for establishing a desired value of one of said first and second dimensions when said workpiece is leaving said stand afler a predetermined passage of said workpiece,

and means for establishing a roll-opening position correction in reference to said first and second dimensions of said workpiece relative to said first and second passages of said workpiece through said stand for effecting said desired value of said one dimension after said predetermined workpiece passage through said stand.

8. The apparatus of claim 7, with said first dimension being the length dimension of said workpiece,

said second dimension being the delivery height of said workpiece.

9. In apparatus for determining the roll setting position of at l0 least one stand of a rolling mill operative with a workpiece, the

combination of:

means for measuring a first dimension of said workpiece after each of a predetermined first measurement pass by said rolling mill and a predetermined second measurementtpass operation by said rollin rnill,

means or determining a second imenslon of said workpiece in relation to the operation of said stand during each of said first measurement pass operation and said second measurement pass operation, means for establishing the desired delivery height of said workpiece after a predetermined pass through said stand,

means for determining a roll setting position calibration correction in relation to a comparison of said measured first and second dimensions in accordance with the respective first and second measurement pass operations,

and means for establishing a roll setting position in relation to said calibration correction and said desired delivery height.

10. In a method operative with at least one rolling mill stand having a pair of rolls and operative with a workpiece, the steps of:

establishing a first selected characteristic of said workpiece after a first predetermined reduction passage of the work piece between said rolls,

establishing a second selected characteristic of said workpiece after a second predetermined reduction passage of the workpiece between said rolls,

relating the selected characteristic established afler said first passage to the selected characteristic established after said second passage to determine an error condition of said rolling mill stand,

establishing a desired height for said workpiece after a predetermined last passage through said stand,

and controlling the operation of said rolling mill stand in relation to said error condition and said desired height.

ll. The method of claim 10, with said first selected characteristic being a resulting predetermined dimension of the workpiece after the first reduction passage,

and with said second selected characteristic being a resulting predetermined dimension of the workpiece after the second reduction passage.

12. The method of claim [0, wherein the respective volumes of said workpiece after each of said first reduction passage and said second reduction passage are compared for establishing said error condition,

and correcting the roll setting position of said rolling mill stand in accordance with said error condition for providing a substantially desired thickness workpiece after at least said predetermined last passage of the workpiece between said rolls.

t i 8 i ll 

1. In apparatus for controlling at least one stand of a rolling mill having a screwdown position control apparatus and a pair of rolls operative with a workpiece, the combination of; means for establishing the delivery length of the workpiece after a first passage through at least said one stand of the rolling mill, means for establishing the roll separating force and screwdown position of at least said one stand during said first passage, means for establishing the delivery length of said workpiece after a second passage through at least said one stand of the rolling mill, means for establishing the roll separating force and screwdown position of at least said one stand during said second passage, and means for determining the calibration of said screwdown position control apparatus using a predetermined workpiece volume relationship relative to said first aNd second passage through the rolling mill.
 2. The apparatus of claim 1, including said means for determining the calibration of said screwdown position control apparatus being operative with the assumption that the workpiece width remains substantially the same during said first and second passage.
 3. The apparatus of claim 1, including said means for determining the calibration of the screwdown position control apparatus using nominal width and a prediction of the increase in width during rolling.
 4. In apparatus for controlling a rolling mill having a pair of rolls operative with a workpiece, the combination of: means for establishing the delivery length and width of said workpiece after a first passage through said rolling mill, means for establishing the roll separating force and screwdown position, of said rolling mill during said first passage, means for establishing the delivery length and width of said workpiece after a second passage through said rolling mill, means for establishing the roll separating force and screwdown position of said rolling mill during said second passage, means for determining the calibration of the rolling mill screwdown position using a predetermined workpiece relationship between the first and second passage through the rolling mill.
 5. In apparatus for controlling at least one stand of a rolling mill having a pair of rolls operative with a workpiece, the combination of: means for establishing the value of a selected dimension of said workpiece after a first reduction of said workpiece by passing said workpiece between the rolls of said rolling mill, means for establishing the value of said selected dimension of said workpiece after a second reduction of said workpiece by passing said workpiece between the rolls of said rolling mill, means for establishing an operational error condition of at least said one stand in relation to said selected dimension established after said first reduction and said selected dimension established after said second reduction, means for predicting a desired value of said selected dimension after a predetermined pass of said workpiece between said rolls, and means for establishing the roll opening position of at least said one stand during said predetermined pass in accordance with said operation error and in accordance with said desired value of said selected dimension.
 6. The apparatus of claim 5, with said selected dimension being the length dimension of said workpiece, and with said predetermined pass being a subsequent pass of said workpiece between said rolls.
 7. In apparatus for controlling the roll opening position of a rolling mill stand operative with a workpiece, the combination of: means for measuring a first dimension of said workpiece after each of a first passage through said stand and a second passage through said stand, means for establishing a second dimension of said workpiece after each of said first passage and said second passage in relation to the stand roll forces during the respective first passage and second passage through said stand, means for establishing a desired value of one of said first and second dimensions when said workpiece is leaving said stand after a predetermined passage of said workpiece, and means for establishing a roll-opening position correction in reference to said first and second dimensions of said workpiece relative to said first and second passages of said workpiece through said stand for effecting said desired value of said one dimension after said predetermined workpiece passage through said stand.
 8. The apparatus of claim 7, with said first dimension being the length dimension of said workpiece, said second dimension being the delivery height of said workpiece.
 9. In apparatus for determining the roll setting position of at least one stand of a rolling mill operative with a workpiece, the combination of: means for measuring a first dimenSion of said workpiece after each of a predetermined first measurement pass by said rolling mill and a predetermined second measurement pass operation by said rolling mill, means for determining a second dimension of said workpiece in relation to the operation of said stand during each of said first measurement pass operation and said second measurement pass operation, means for establishing the desired delivery height of said workpiece after a predetermined pass through said stand, means for determining a roll setting position calibration correction in relation to a comparison of said measured first and second dimensions in accordance with the respective first and second measurement pass operations, and means for establishing a roll setting position in relation to said calibration correction and said desired delivery height.
 10. In a method operative with at least one rolling mill stand having a pair of rolls and operative with a workpiece, the steps of: establishing a first selected characteristic of said workpiece after a first predetermined reduction passage of the workpiece between said rolls, establishing a second selected characteristic of said workpiece after a second predetermined reduction passage of the workpiece between said rolls, relating the selected characteristic established after said first passage to the selected characteristic established after said second passage to determine an error condition of said rolling mill stand, establishing a desired height for said workpiece after a predetermined last passage through said stand, and controlling the operation of said rolling mill stand in relation to said error condition and said desired height.
 11. The method of claim 10, with said first selected characteristic being a resulting predetermined dimension of the workpiece after the first reduction passage, and with said second selected characteristic being a resulting predetermined dimension of the workpiece after the second reduction passage.
 12. The method of claim 10, wherein the respective volumes of said workpiece after each of said first reduction passage and said second reduction passage are compared for establishing said error condition, and correcting the roll setting position of said rolling mill stand in accordance with said error condition for providing a substantially desired thickness workpiece after at least said predetermined last passage of the workpiece between said rolls. 